This hearing test measures the relative sensitivity of your ears at different frequencies. It produces equal loudness contours or hearing sensitivity curves – the frequency response of your own ears.
The flash script allows you to play sound files with a range
of frequencies and sound levels with the click of a mouse.
The total size of all files is approximately 400 k. Because
both the chart and the instructions refer to decibels,
you may wish to go first to What
is a decibel?

Warning 1. Do not start with a panel
in the top third of the chart: you might hurt or even damage your ears.

Warning 2. Results using this test
cannot be regarded as clinical data. Although the sound
files have been carefully prepared, the actual sound level
and spectral purity depend on the frequency response of your
sound card and headphones. They may, however, be helpful for
comparison, such as left vs right ear, or for changes in hearing
over time, assuming that you use the same hardware. Note,
however, that daily fluctuations in hearing are common. If
you are worried about your hearing, consult an audiologist.

For best results you will need reasonably good quality headphones
that enclose your ears completely and seal out external
noises. Ordinary loudspeakers, and especially the small ones
that come with computers, have such poor response, particularly
at low frequency and are so much affected by interference
effects and resonances that results obtained with them are
useless. They may also be damaged by low frequencies.

The instructions for using this service are given
below the graphic. Repeat: do not start in the top third of the chart.

Repeat: do not start in the top third of the chart.

How to use this web service to measure equal loudness curves.

Minimise any background noise: turn off machinery, close windows
etc. If your computer has a fan, you may be able to put it under the
desk.

Plug headphones into your soundcard output and put them on, making
sure that they seal well around your ears.

In the 1 kHz column, choose a panel about halfway down. Listen to
it and check that (i) it is not uncomfortably loud and (ii) it is
considerably louder than the background noise. Go up or down the column
if necessary until these conditions are satisfied. Notice that the
dB level chosen is now recorded at the bottom of the chart. Once you
have made a choice, this becomes your reference sound.

In the 750 Hz column, click the panel next to your reference panel.
If you find that it is less loud than the reference sound, click on
the panel that is 3 dB louder, still at 750 Hz. (Conversely, it is
is louder, click on the panel below to make it softer. And if it is
equally loud, leave it where it is.) Go back to your reference sound
and compare. Keeping doing this until you are satisfied that the the
750 Hz and the 1 kHz sounds are equally loud. (You may find it difficult
to judge equal loudness for different pitches, but because loudness
is by definition subjective, there is no person or machine that can
do it for you.)

Next find a sound at 500 Hz whose loudness equals that of your reference
sound at 1 kHz.

Do the same for 375, 250 Hz etc, all the way down to 30 Hz, at
all times using 1 kHz as the reference.

Now find a sound at 1.5 kHz that equals the loudness of the 1 kHz
reference. Continue to 2, 3 etc up to 16 kHz.

The chart will now show the sounds that you have chosen as having
equal loudness. We repeat that, while this curve roughly approximates
the frequency response of your ears, it is modified by the frequency
response of your sound card and headphones. You can print this chart
by right clicking on the chart, by going to the 'file' menu of your
browser and clicking 'print', or you can print the screen electronically.

You might like to compare your curve to the standard equal loudness curves
(below) and to the dBA weighting curve given on What
is a decibel? The dBA weighting curve is the response of a filter
that is applied to sound level meters to mimic (roughly) the response
of human hearing. So a typical human equal loudness curve is somewhat
similar to the dBA curve, but inverted.
The values on the graph you have made will be arbitrary (unless you
calibrate them – see below), because we do not know the properties
of your sound card and headphones.

What does your hearing curve mean?

Most people will find that their hearing is most sensitive around 1–4 kHz and that it is less sensitive at high and low frequencies. Children
usually hear 16 kHz moderately well. The high frequency hearing of adults
depends on age and exposure to loud sounds. It is not uncommon for adults
to have very low sensitivity for the highest frequencies. (Your children
may be complaining about that 16 kHz tone that you cannot hear.) If you
cannot hear the lowest frequencies, it's probably because you are using
loudspeakers. As we mentioned above, you need headphones that enclose
your ears for this.

How does your hearing response depend on loudness?

The shape of your hearing response curve probably depends on loudness.
For most of us, the curve is flatter at higher sound levels*. Choose a
louder or softer reference signal and obtain a new curve. (If you reload
the page it will clear the old curve from the screen.)

Can you use this web service to measure hearing threshold curves?

It is possible, but not likely. Even if your headphones seal really well
around your ears, they will probably only give you about 20 to 25 dB insulation
from the external sound field. Human hearing thresholds can be around
0 dB in the frequency range 0–4 kHz. It is rare to find an office whose
sound level is as low as 20 dB – i.e. an office in which 20 dB of insulation
would reduce the sound level to near threshold levels. For a start, your
computer probably has a fan and a power supply that raise the sound level
above 20 dB, even at these frequencies. There may be other background
noise as well. However, under very good conditions (a really quiet, still
environment, no computer fan or other stray noises) it might be possible.

If so, the method would be to find the lowest sound level audible
at each frequency. (How this level relates to the common standard of
sound levels (see What
is a decibel?) is something that we cannot tell you: it depends
on the gain of your sound card and headphones. However, see the note
about calibration below.)

Under normal conditions, if you seek the lowest sound level you can
hear at each frequency, what you will find is the lowest level of a
sine wave that is not masked by the background noise that you are hearing
inside your headphones.

This graph, courtesy of Lindosland, shows the 2003 data from the International Standards Organisation for curves of equal loudness determined experimentally. Plots of equal loudness as a function of frequency are often generically called Fletcher-Munson curves after the original work by Fletcher, H. and Munson, W.A. (1933) J.Acoust.Soc.Am. 6:59.

What does zero dB mean? It is, by definition, the reference level and is arbitrary. For the hearing curve you make with the gadget above, it is the maximum output of your interface card, amplifier and earphones with the current settings. (We do not know the specifications of your equipment, of course, and we don't know how high you have set the 'volume' knob.) For the graphs shown immediately above, 0 dB is 20 µPa. See What is a decibel? for an explanation.

Calibration and improvements. It is possible to improve the accuracy of measurements
made using this service by calibrating the response of your sound card
and headphones, using a small microphone with good frequency response.
(Microphones usually have much flatter frequency response than do speakers,
so even a quite cheap electret microphone can be useful.) Connect the
microphone to an oscilloscope or to the input of the sound card of a
second computer. Using high but not painful sound levels, play sound
files with the same amplitude (i.e. click on panels in the same row) and
measure the variation in the recorded AC voltage for different frequencies.
This works at low frequencies, but for the highest frequencies the sound
level varies considerably within the headphone itself. Microphones often
come with a calibration curve, or a sensitivity rating in volts/pascal.
Using this you can convert the values measured with the microphone to
the standard expressions of sound level, in dB with respect to 20 µPa.

* The flattening of the hearing curve at high sound
levels is sometimes referred to jokingly as the first law of hifi: if
you turn it up it sounds better. If ever you compare hifi systems in
a shop, vary the volume controls (and loudness control, if present).
The sales staff are usually aware of this law, so, before you buy, make sure that you try turning the expensive one down
so that it slightly softer than the cheap one.

The flash script above was made by George Hatsidimitris with sound
files by John Tann of the School of Physics, UNSW. John has posted an array of
sound files over a range of sound levels and frequencies.